Bacteria Producing Antibiotics in Caves: Friends or Foe?

Caves contain an abundance of Actinobacteria, which can be valuable sources of novel antibiotics to replace those currently ineffective. Our study explores secondary metabolites produced by cave bacteria.  One aim of this study is to determine how many different kinds of antibiotics are being produced by the bacterial inhabitants of the yet untapped extreme aphotic, oligotrophic cave ecosystem. We hypothesize that antibiotic production varies with increasing depth. This study also aims to provide insight into whether antibiotics are produced in nature as components of signaling or weaponry.  Isolates from four semi-arid carbonate caves (Carlsbad Cavern, Back Country Cave, Spider Cave, and Lechuguilla) in Carlsbad National Park have been tested for antibiotic production using an agar diffusion protocol utilizing seven common BSL2 pathogens.  Of the isolates tested for antibiotic production, <20% appeared to inhibit pathogen growth, with the most frequently inhibited pathogens; Klebsiella pneumoniae, Proteus vulgaris, Shigella flexneri and Streptococcus pneumoniae.  From this set of producers, isolates were streaked against each other to identify the production of similar or different compounds.  Of these, 20 displayed zones of inhibition ranging from 0.3-2cm and revealed three potentially different compounds. The next step is to test the isolates producing different compounds against common antibiotics.  Results from these tests will identify a core set of isolates to explore genes and secondary metabolite pathways associated with antibiotic production. These experiments will provide insight into the special properties of cave-adapted bacteria and help delineate their potential for antibiotic synthesis.